1. Field of the Invention:
The present invention relates to a highly acoustical auto ceiling panel and its manufacturing process.
2. Description of the Prior Art:
The conventional auto ceiling panel is a three-layer structure in which a metal lath is sandwiched between polyethylene foams with isolated air bubbles, said metal lath being thermally fused to these foams or it is a four-layer structure in which a metal lath is sandwiched between a polyethylene foam with a vinyl chloride sheet and another polyethylene foam. In such laminated (three-layer or four-layer) structures the heat insulation and safety to the human body are fully assured, but on account of the polyethylene foam having isolated air bubbles, the soundproofing of the interior noise is not well assured.
It has been known that provision of holes through auto ceiling panel would improve the acoustical characteristic thereof. In such three-layer or four-layer structure the presence of said metal lath sandwiched between polyethylene foams hinders the boring of such through holes with an acoustical effect and it is impossible to bore such through holes after lamination is done.
For these reasons, the conventional practice is to bore through holes separately on each polyethylene foam to be pasted together and thereafter laminate the foams on both sides of the metal lath. Even in this practice it is difficult to laminate the upper and lower foams with identical pattern with the result that a very few through holes running in both foams are obtained and a prominent effect of absorbing the sound is not secured for all the trouble of working.